The passive optical network (PON) refers to an optical network which does not include any electronic devices or electronic power supply in its optical distribution network (ODN). A PON system is mainly consisted of an optical line terminal (OLT) on an office end, optical network units (ONUs) or optical network terminals on user ends, and an ODN between the OLT and the OUNs/ONTs. The ODN only includes passive devices without expensive active electronic devices. The PON is a promising solution because the PON eliminates active devices between the office and the user end so as to enable an easier maintenance, a higher reliability, a lower cost and optical fiber resources saving.
Two main technologies currently used in broadband access in the PON include EPON and GPON. In the description below, the EPON and its derived networks (such as GEPON, 10G-EPON) are collectively called as EPON type networks, while the UPON and its derived networks (such as GPON, XGPON and NGPON2) are collectively called as EPON type networks.
IEEE 1588 PTP is a high precision timing protocol which is widely used in mobile backhaul network for time and frequency synchronization. Nowadays, as one of the mobile backhaul network element, PON system (such as GPON, XGPON and NGPON2) was also supposed to support IEEE 1588 PTP in SO-OC mode. FIG. 1 illustrates a schematic drawing of an IEEE 1588v2 PTP solution in an existing GOPN system. As shown in FIG. 1, first, the OLT at the office end, as an IEEE 1588 slave, receives and terminates IEEE 1588 messages from network side. Then time and clock information will be transferred from the OLT to ONUs via ToD over UPON protocol which is defined in ITU-T G.984.3 Amendment 2. At last, the ONUs/ONTs, as IEEE 1588 masters, re-package the time/clock information (received from PON interface) into 1588 messages and deliver them to UNI interface towards the base stations. There are similar structures in the EPON as that in the GPON.
OMCI which is a configuration transmission channel defined in the GPON standard transmits OMCI messages by establishing private OMCI management channels between the OLT and the OUNs/ONTs, which provides a standard ability to acquire the OUNs/ONTs and also can manage and control the OUNs/ONTs.
In the EPON type networks, the management and maintenance to the OUNs/ONTs by the OLT is done through an OAM protocol defined in the IEEE 802.3ah.